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Glossary

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A

AQS - Air Quality System
EPA's repository of ambient air quality data. AQS stores data from over 10,000 monitors, 5000 of which are currently active. State, local and tribal agencies collect the data and submit it to AQS on a periodic basis.

AQS Data Mart
The AQS Data Mart is a database containing all of the information from the AQS system. The AQS Data Mart was built as a storehouse of air quality information that allows users to make queries of unlimited quantities of data.

Accuracy
the degree of closeness of measurements of a quantity to that quantity's actual (true) value

Air quality data
the amount of pollution and other substances present in the atmosphere measured by monitors throughout the nation

Air Monitoring
sampling for and measuring of pollutants present in the atmosphere

AirNow
an EPA program that provides the public with easy access to national air quality information via the Internet. AIRNow offers daily Air Quality Index (AQI) forecasts as well as real-time AQI conditions for over 300 cities across the United States and provides links to more detailed state and local air quality web sites.

Air Quality Index (AQI)
a numerical index used for reporting severity of air pollution levels to the public. The AQI incorporates five criteria pollutants -- ozone, particulate matter, carbon monoxide, sulfur dioxide and nitrogen dioxide -- into a single index. AQI levels range from 0 (Good air quality) to 500 (Hazardous air quality). The higher the index, the higher the level of pollutants and the greater the likelihood of health effects. The AQI incorporates an additional index category -- unhealthy for sensitive groups such as children and people with asthma -- that ranges from 101 to 150. In addition, the AQI comes with detailed health cautions.

Ambient Air
the portion of the atmosphere external to buildings and breathed by the general public

Attainment area
a geographic area that meets or does better than the national standard set by the federal government; areas that don't meet the national standard are called nonattainment areas (also see National Ambient Air Quality Standards - NAAQS)

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B

Baseline Year
the year to which other years are compared

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C

CBSA - Core Based Statistical Area
a U.S. geographic area defined by the Office of Management and Budget (OMB) based around an urban center of at least 10,000 people and adjacent areas that are socioeconomically tied to the urban center. Metropolitan and Micropolitan Statistical Areas are the two categories of Core Based Statistical Areas.

CSV - comma separated variable format
a tabular format designed for importing into spreadsheets or other data processing software

Carbon Monoxide (CO)
a colorless, odorless gas resulting from the incomplete combustion of hydrocarbon fuels. CO interferes with the blood's ability to carry oxygen to the body's tissues and results in numerous adverse health effects. Over 80 percent of the CO emitted in urban areas is contributed by motor vehicles. CO is a criteria air pollutant.

Clean Air Act
The original Clean Air Act, signed into law by President Lyndon B. Johnson in 1963, was considered to be the first modern environmental law enacted by the United States Congress. The Clean Air Act of 1970, reviewed and amended by Congress in 1975, 1977, and 1990, has formed the basis of the current federal air pollution control program.

Continuous Monitor
a device which allows ambient PM mass concentrations to be monitored in near- real-time for extended periods

Criteria Air Pollutant
six common air pollutants regulated by the EPA on the basis of certain criteria (namely, information on public health and/or environmental effects of pollution). The criteria pollutants are carbon monoxide (CO), lead (Pb), ozone (O3), particulate matter (PM), sulfur dioxide (SO2), and nitrogen oxides (NOx). They are regulated under EPA's National Ambient Air Quality Standards (NAAQS).

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D

Daily Max
the highest value measured at a monitor on a given day

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E

Emissions
released or discharged air contaminants in the ambient air from any source

Estimated Exceedances
Calculated number of days in the year when values are estimated to exceed the level of the National Ambient Air Quality Standards (NAAQS), after compensating for days when scheduled monitoring did not occur

Exceedance
a measured level of an air pollutant higher than the National Ambient Air Quality Standards (NAAQS). (The violation of a national ambient air quality standard is based on multiple years of data, so monitoring an exceedance does not necessarily mean that a violation of the standard has occurred.)

Exceptional events
unusual events including high winds, fires, and construction that, in certain cases, can be excluded from calculations related to the National Ambient Air Quality Standards (NAAQS). However, for the purposes of counting unhealthy days, it is important to consider all monitored values including those caused by exceptional events because they represent the actual pollution in the air.

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F

Fine Particulate Matter (PM 2.5)
particulate matter 2.5 microns or less in diameter

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G

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H

Hazardous Air Pollutants (HAP)
pollutants that cause or may cause cancer or other serious health effects such as reproductive effects or birth defects, or adverse environmental and ecological effects. The EPA has listed 188 hazardous air pollutants. Examples include benzene (found in gasoline), perchlorethlyene (used in some dry cleaning facilities), and methylene chloride. Also called Toxic Air Pollutants or Air Toxics.

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I

IMPROVE - Interagency Monitoring of Protected Visual Environments
a program developed as a collaborative effort between the US EPA and the National Park Service in order to establish the chemical composition of haze in National Parks and to restore visibility

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J

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K

KML - Keyhole Markup Language
a computer language used to describe three-dimensional geospatial data for display in application programs

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L

LC
local conditions of temperature and pressure

Lead (Pb)
a metal found naturally in the environment as well as in manufactured products. The major sources of lead emissions have historically been from fuels in on-road motor vehicles (such as cars and trucks) and industrial sources. Lead is considered both a criteria air pollutant and a hazardous air pollutant (air toxic).

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M

Mobile Sources
sources of air pollution such as cars, motorcycles, trucks, off-road vehicles, boats and airplanes (See also stationary sources)

Monitor
a device that periodically or continuously samples air pollutants in the ambient air or from individual pollution sources. Within AirData and related data systems, the term “monitor” does not indicate a physical instrument. Rather, any time a parameter is measured at a site, a “monitor” is created for that parameter. For example, if a sampler collects air that is analyzed for 12 different parameters, then it is listed as 12 separate monitors. So the term monitor denotes that a time series of measurements for a parameter is available at a site. A monitor is indicated by the code or name of the parameter measured. If the parameter is measured more than once at a site, it is differentiated by the POC.

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N

NATTS - National Air Toxics Trends Stations
a monitoring network operated by state and local agencies to assist in the EPA goal of eliminating unacceptable health risks associated with exposure to air toxics and to substantially reduce or eliminate the adverse effects of air toxics on the environment

NCORE
a multi pollutant monitoring network that integrates several advanced measurement systems for particles, pollutant gases, and meteorology

National Ambient Air Quality Standards (NAAQS)
a level of outdoor air quality set by the EPA to protect human health and public welfare. Standards have been set for six common pollutants: carbon monoxide, lead, nitrogen dioxide, particulate matter, ozone, and sulfur dioxide.

Nitrogen Oxides (Oxides of Nitrogen, NOx)
a general term pertaining to compounds of nitric oxide (NO), nitrogen dioxide (NO2) and other oxides of nitrogen. Nitrogen oxides are typically created during combustion processes and are major contributors to smog formation. NOx is a criteria air pollutant and may result in numerous adverse health effects.

Nonattainment area
a geographic area that does not meet the national standard set by the federal government; areas that meet the national standard are attainment areas. It is possible for an area to be in attainment for one pollutant, but non-attainment for a different pollutant (also see National Ambient Air Quality Standards - NAAQS).

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O

Ozone
a reactive chemical gas consisting of three oxygen atoms. Ozone is created when oxides of nitrogen (NOx) and volatile organic compounds (VOCs) react in the presence of sunlight. Ozone is protective in the upper atmosphere (stratosphere). Ozone in the troposphere (ground-level ozone) causes numerous adverse health effects and is a criteria air pollutant. It is a major component of smog.

Ozone Precursors
chemicals in the atmosphere that react to form ozone. Nitrogen oxide compounds (NOx) and volatile organic compounds (VOCs) are ozone precursors. Emissions from industrial facilities and electric utilities, motor vehicle exhaust, gasoline vapors, and chemical solvents are some of the major sources of NOx and VOC.

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P

POC - Parameter Occurrence Code
a code number used to identify when more than one monitor is measuring the same parameter at a site

PPB - parts per billion
1 part in 1,000,000,000 by volume

PPM - parts per million
1 part in 1,000,000 by volume

Parameter
a pollutant or other chemical substance (or wind speed or temperature) that is measured at a site. EPA creates new parameter names (and codes) for the same substance if the methods being used for measurement are different enough that results are not comparable. For example, in 2006 PM2.5 measured using continuous methods was given a different parameter name than PM2.5 measured intermittently on filters.

Particle Pollution
fine liquid or solids such as dust, smoke, fumes, or smog found in air or emissions

Particulates/Particulate Matter (PM)
solid particles or liquid droplets suspended or carried in the air. Particulate matter is a criteria air pollutant and is regulated as PM2.5 and PM10.

PM2.5
tiny particles with an aerodynamic diameter less than or equal to 2.5 microns. This fraction of particulate matter penetrates most deeply into the lungs. Also called fine particle pollution

PM10
small particles with an aerodynamic diameter less than or equal to 10 microns (about 1/7 the diameter of a single human hair)

Point Sources
large, stationary sources of air pollution such as factories and power plants

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Q

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R

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S

Sensitive Groups
subsets of the general population that are at greater risk than the general population to the toxic effects of a specific air pollutant (e.g., infants, asthmatics, elderly)

Site
a geographic location where one or more monitors operate. Also called monitoring stations or facilities. Sites are identified in AirData and related systems by a 2-digit State Code, a 3-digit County Code, and a 4-digit site code within the county. The codes are separated by hyphens.

Smog
a combination of smoke, other particulates, and ozone which may result in a murky brown haze that causes adverse health effects

Source
any place or object from which air pollutants are released. Sources that are fixed in space are stationary sources and sources that move are mobile sources

Stationary Source
non-mobile sources such as power plants, refineries and manufacturing facilities which emit air pollutants.

Speciated Data
the components that make up fine particle pollution. PM2.5 species are sulfates, nitrates, organic carbon, elemental carbon, crustal, and un-attributed mass (the difference between measured PM2.5 and the sum of the other five components).

Sulfur Dioxide (SO2)
a strong smelling, colorless gas that is formed by the combustion of fossil fuels. SO2 is a criteria air pollutant

Sulfur Oxides
pungent, colorless gases (sulfates are solids) formed primarily by the combustion of sulfur-containing fossil fuels, especially coal and oil

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T

TSP - Total Suspended Particulates
refers to respirable and larger particle pollution

Time Series Plot
a sequence of data points measured at successive times spaced at uniform time intervals

Toxic Air Pollutants
see hazardous air pollutant

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U

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V

Violation
when calculations based on multiple years of monitored data exceed the National Ambient Air Quality Standards (NAAQS)

Volatile Organic Compounds (VOC)
organic compounds that vaporize (become a gas) at room temperature. VOCs contribute significantly to ground-level ozone pollution

W

Weighted Annual Mean
a mean calculated by first averaging values for each calendar quarter, then averaging the four quarterly averages. (This is done so each quarter of the year is weighted equally even if more sampling is done during a particular quarter.)

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X

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Y

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Z

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